1. Field of the Invention
This invention relates to a perlite sound absorbing plate composed of an aggregate formed of foamed perlite particles, bonding agent formed of cement and liquid rubber latex and having an excellent sound absorbing property and capability of preventing the sound absorbing property from deteriorating under water absorbed condition and a sound insulating wall constructed by arranging a number of said perlite sound absorbing plates side by side and by assembling together them into one integral body.
2. Description of the Prior Art
A porous sound absorbing material containing a lightweight aggregate has recently been used as a sound absorbing material for preventing public nuisance caused by noises. Some of these porous sound absorbing materials makes use of a main aggregate formed of perlite. Such sound absorbing material containing the main lightweight aggregate formed of perlite can eliminate the drawback of less durability which has been encountered with the prior art sound absorbing material formed of textile such as glass wool, rock wool or the like and can be set in place without using any box-shaped flame.
The foamed perlite particles are an aggregate which is significantly light in weight. As a result, the foamed perlite particles have been expected to be used as the sound absorbing material. In addition, it has been ascertained that the porous sound absorbing material can be obtained by bonding the foamed perlite particles by means of a bonding agent.
The inorganic textile sound absorbing material exhibits a high acoustic absorptivity of at least 80% over a wide frequency range. The sound absorbing material containing the lightweight aggregate such as perlite or the like, however, could not exhibit such a high acoustic absorptivity. In addition, the sound absorbing material containing the lightweight aggregate such as perlite or the like could not recover lost sound absorbing property under the water absorbed condition due to rain or the like when the material is used outdoors.
The inventors have recognized the above mentioned drawback of the perlite sound absorbing material and developed a novel perlite sound absorbing plate which makes use of cement as its bonding agent and which can exhibit a high acoustic absorptivity over a wide frequency range even under a water absorbed condition.
The cement bonding agent has water absorbing and retaining property which is higher than that of any other organic or inorganic bonding agents and hence causes the sound absorbing property of the perlite sound absorbing material to deteriorate. In addition, the cement bonding agent has a large specific gravity which makes the perlite sound absorbing material inconvenient in handling. Moreover, the perlite sound absorbing plate containing the cement bonding agent is difficult to be molded, and as a result, such sound absorbing plate could not be used in practice at present.